trogdor113

I searched and found a few threads that might be related, but none of them ended conclusively:

2009 LS 460 seat heater
Seat Heater Won't Stay On...
Seat heater works then blows cold air

In my '08 600h the driver's seat heat comes on when the car is first started. Both the cushion and back get nice and warm and I'm a happy camper. However, after some indeterminate amount of time the seat begins to cool. The LED on the switch remains on and green, but the seat feels as though temperature is no longer being maintained.

I've been reading through TIS and I found service bulletin L-SB-0041-10 regarding seat heat turning off. This definitely applies to my VIN (1674) but it seems like a weird fix. There's also no updated part number like there is for the air suspension struts. I initially thought this was dictating replacement of the control modules, but as I've looked into this more I now think this is actually talking about the Peltier element/fan unit, one each for cushion and back.

Has anyone experienced this issue and resolved it with this fix? It's a bit of a pain to remove the seats from the car, so I'd like to know that this will work before I go to the trouble. I've attached the bulletin in question, and an extract from the "New Car Features" describing the seat climate system of the LS600hL.

trogdor113

I guess no one has run into this then.
If I correctly understand the seat climate system, the heat pads only activate for the first 10 minutes or so, after which the internal air circulation takes over with heat from the two Peltier elements. I guess the intent was longevity of the heating elements? Anyway, I found a wrecker selling the entire ductwork for the seat from a later car, so once that arrives I'll be replacing my parts.

trogdor113

Confirmed today that this addresses the problem. I installed "new" climate controller parts from a 2013 LS and the seat is now staying nice and toasty the whole time. A few things worth noting:

• The '13+ seat internals are indeed different from at least the '07 - '09 seats (I would imagine the '10 - '12 as well). The electrical connecters plug in fine, the duct sizes are the same, and the ports in the seat foam are the same. However, the thermal units mount in a different, incompatible way and the duct routing is different in terms of bends and length. I used the existing ductwork from my seat and mounted the units with zip ties. Sounds janky, but there's no force applied to the parts and it's quite secure in there.
• The seats have to come completely out of the car. You could manage the seatback unit in the car but the cushion unit is nestled far too deeply to access. Removal from the car isn't a big deal, but you will want a helper to avoid damaging trim and bodywork.
• Removing the seat cushion is also not "hard", but it is fiddly and cramped. Lots of screws and connectors to remove, and lots of potentially fragile plastic. A little patience will go a long way.

I didn't get any pictures, but I've confirmed I need to do the passenger seat as well. I'll document the process when I repair that side.

miket000

A few years back I purchased a spare Peltier element for my 460 seat back. I planned on replacing it to address the intermittent cooling of my seats. Unfortunately I never got around to swapping it out.

Thank you for your post. It sounds like replacing the elements with 13+ is the way to go.
For your drivers seat did you replace the 2 Peltier elements along with the controller? I assume the controller is mounted in the seat. Total of 3 new components per seat?

trogdor113

No, only the Peltier elements. My initial reading of the service bulletin had made me think that I needed to replace the blower and/or control module, but the actual part numbers in the bulletin are only the thermal units themselves. I've been on several longer drives since installing these in my seat and the seat cushion especially gets hot. I can't speak to the cooling since it's in the 20s F here 😉

There is a dedicated ECU for the heating and cooling in each seat, yes. It's located in the bottom half of the seat, next to the blower unit. I didn't pay attention to it really when I did this job, but the manual has it as one of the last things to be removed in disassembling the seats.